Question PCIe - question about "lanes" XX/YY

[franekw]

Hello,

I am collecting information for a new build based on Intel 9700K, 32 GB 3200, Asus ROG Strix RTX2080 Super and all this I want to put on ASUS PRIME Z-390A . I came across things like PCIe 16/0, PCIe 8/8, etc. If you look at the spec of the motherboard, there is info related to expansion slots:

Spoiler: ASUS Prime Z-390 A - Expansion slots

2 x PCIe 3.0/2.0 x16 (x16, x8/x8, x8/x4+x4 (), x8+x4+x4/x0 () (1)
1 x PCIe 3.0/2.0 x16 (max at x4 mode) *4
3 x PCIe 3.0/2.0 x1
* For 2 SSD on CPU support, install a Hyper M.2 X16 card (sold separately) into the PCIeX16_2 slot, enable this card under BIOS settings.
** For 3 SSD on CPU support, install a Hyper M.2 X16 card (sold separately) into the PCIeX16_1 slot, enable this card under BIOS settings.

*1 PCIEX16_1 slot supports up to 3 Intel® PCIe NVME SSDs via a Hyper M.2 X16 series Card. *3
*2 PCIEX16_2 slot supports up to 2 Intel® PCIe NVME SSDs via a Hyper M.2 X16 series Card. *3
*3 Hyper M.2 X16 series card sold separately. Install a Hyper M.2 X16 series card and enable this card under BIOS settings.
*4 The PCIe x16_3 slot shares bandwidth with SATA_5 and SATA_6. The PCIe x16_3 is default set at x2 mode.
*5 The M.2_1 socket shares bandwidth with SATA_2 port when using M.2 SATA devices. Adjust BIOS settings to use a SATA device.
*6 Only available under Windows® 10.

I have a few questions?
If I read it correctly, it means that if I insert a video card that takes speed of 16 lines, then the slot is going to take the whole available speed and other two slots are disabled, am I correct? Do I control such configurations per PCIe slot somewhere, in BIOS or is it "claimed" by device? I can also see slot 3 is already at max speed 4 so its only impact is on slot two which can be at speed 8 or 4.

Thanks

PS> Link to my build:
https://pcpartpicker.com/user/franekw/saved/#view=L479GX

 

[kanewolf]

Not quite an accurate interpretation. If you have one card it will get 16 lines. If you have two cards installed, each will get 8 lines. You usually have no explicit control of allocations.

 

[franekw]

Hi, kanewolf and thanks for your help.

I have a two questions as I am still confused. Why does specs provide such different configurations as x8/x8, x8/x4+x4 x8+x4+x4/x0 ?

Let's say I put another card in the slot PCIe1_2. Is 8 lines enough for any modern video card, such as Asus RTX2080 Super if I install something else in the second PCIe slot?

Thanks

 

[kanewolf]

I don't game, so I don't really keep up with what percentage there is for running a 2080 at x8.

The specs are trying to tell you what the behavior of the board is Two cards gets you x8 and x8. Three cards gets you x8, x4 and x4.